1. Field of the Invention
The present invention relates to ATA multiplexed communications for land vehicles and particularly relates to multiplexed communications with intelligent controls for tractor-trailers which conforms to the Society of Automotive Engineers' recommended practices for covered functions. A copy of the SAE J 1708 draft recommended practice for serial data communications between microcomputer systems in heavy duty land vehicle applications is enclosed and incorporated herein by reference.
2. Description of the Prior Art
Multiplexing to reduce the number of dedicated communication paths or links among transmitters and receivers is very old and is believed to have originated in telephone systems. More recently, as the number of accessories and functions to be performed in land vehicle applications have climbed, multiplexing has been employed in land vehicles. It is believed that the initial vehicular application occurred in military aircraft. Efforts are now being made in the automotive and truck industries to reduce the number of dedicated communication power links with improvements in the cost and reliability of such systems. See for example, the Floyd et al. U.S. Pat. No. 4,639,609 for: Load Current Management System for Automotive Vehicles.
Among the perceived benefits of such a system, are the following: elimination of 90% or more of the cab to chassis wiring circuits and their associated connections; elimination of 75% of the required cab current from that of non-multiplexed land vehicles compared to non-multiplexed land vehicles. Compared to non-multiplexed land vehicles the multiplexed systems provide a reduction of the cab feed circuit size and reduction of the voltage drop in each circuit multiplexed by eliminating about 25 feet of cable, an overall reduction of land vehicle weight; and reduced installation labor.
Multiplexing as a concept relating to land vehicle applications is somewhat amorphous. A fully distributed multiplex system is one in which each driven device such as a head lamp, a tail lamp, etc. is associated with a solid state circuit switch that actually turns the device power on and off in response to being addressed by a single central processor to accomplished their proper operation.
A more limited multiplex system has a central controller that signals various modules which in turn switch power to a driven device. With this type of system, the central controller, preferably located on one of the driven devices, organizes messages to the respective modules to accomplish the proper control of vehicular components. Multiplex systems are a needed and supportable technology used in association with microprocessors to effect vehicle operation. However, vehicle operation occurs in an environment which has been relatively hostile for previous generations of somewhat delicate integrated circuitry. The mere improvement of integrated circuit technology is not sufficient to allow ready application of the improved technology to a land vehicle.
Similarly, logic power switches recently have been developed by a number of manufacturers, some of which allow limited interrogation of the logic to power the switch. A smart switch of this variety has been developed by Motorola Company, Inc. and is provided under Motorola Model No. MPC 1500. When appropriately utilized, this switch may be employed for the gradual energization and de-energization of heavy loads which have previously contributed to the hostility of a vehicular environment to high level integrated circuitry.
When multiplexing is employed, the data link between the distributed components is of critical importance and it would be desirable to ensure the integrity of the communication processes by providing selective redundancy among a plurality of data links. Analogously, it is desirable that the data links themselves, in addition to being routed along differing paths, most preferably should operate in different modes to reduce the chance of a common failure.
Previously, about half the trucks sold in the United States were customized in some significant regard. At one time, a calculation was made that there were 40,000 differing options available for any given truck. It is now believed that the number of option combinations available are somewhat reduced from that figure. In any case, virtually any option change required a hardware change. As a result, it was virtually impossible for a factory to adequately and efficiently test every combination of options. With the proper employment of microprocessor based controls, all changes and varieties may be entered into the microprocessor memory and the testing can be made rapidly and effectively. The appropriate diagnostic menus and the rapid and efficient testing of these options is anticipated to be a considerable economy while significantly enhancing the quality of the product when this approach is taken. Also, stocking in the factory and at the distribution and maintenance levels is significantly reduced.
A number of developments in isolation have been made which are relevant to the present invention of a land vehicle electrical system. Among these developments are microprocessor based engine controls including some diagnostic abilities in automobiles and in trucks. For example, Cummins Engine provides such a diagnostic system under the name of Compucheck. Likewise, Detroit Diesel Allison provides what is called a DDE DDL reader.
As will be described in greater detail hereinafter, the system of the present invention is regarded as multiplexed and employs two major (substantially identical) controller units communicating with each other. Each unit in its respective control area, operates its respective driven devices directly.
By utilizing the system of the present invention, elimination of high current cab switches and other control, panel, and mechanical switches is achieved. Further, the system is compatible with ATA/SE serial data link standards, is compatible with truck operation monitoring systems, increases usable area on the instrument panel for other gauges, modules, etc. and provides on board dianostics with fault isolation.